Photoelectron spectra of infinitenes and topoisomers

The vertical, valence ionization energies of some [12]circulenes (C₄₈H₂₄) topoisomers have been calculated as free molecules in the gas phase using high-level ab initio coupled-cluster method: EOM-DLPNO-CCSD. Their valence electronic structures depend on molecular topology. We have used calculated vertical, valence ionization energies to simulate their UV photoelectron spectra (UPS). HOMO-LUMO bandgaps and the influence of molecular topology on the spectra were also studied. Our results indicate the presence and importance of stabilizing intramolecular π-π stacking interactions and molecular distortion (via strain energy) on electronic structures and UPS spectra. For example, the HOMO ionization energy increases along the sequence: infinitene<Möbius<Kekulene. The results presented may help in identification and analysis of photoelectron spectra of circulenes which can not be obtained in the gas phase, but rather as adsorbed molecules on metal surface.